Tuesday evening, on the cusp of his arrival in Washington, D.C., as the newly-elected Republican senator from Utah, Romney published an op-ed in The Washington Post that amounts to a manifesto of opposition to President Trump. Some of Trump's policies are fine, Romney said in the piece, but his character and style of governing are destructive to American leadership at home and abroad. "The president," he wrote, "has not risen to the mantle of the office."

He added: "I will support policies that I believe are in the best interest of the country and my state, and oppose those that are not. I do not intend to comment on every tweet or fault. But I will speak out against significant statements or actions that are divisive, racist, sexist, anti-immigrant, dishonest, or destructive to democratic institutions."

If he's true to that commitment, Romney will keep plenty busy over the next two years. The president lives and breathes divisive, racist, sexist, anti-immigrant, dishonest, and destructive behavior. Is any particular tweet significant? Maybe not, but together they weigh heavily on the politics of the moment.

Romney's op-ed could be a significant development: Any truly effective resistance to Trump's presidency is going to require Republican participation sooner or later. Romney — a former governor, the son of a former governor, and the party's 2012 presidential nominee — is GOP royalty. And he's well-positioned to take a stand: He's not likely to make another run for the presidency, but his Utah constituents are notoriously disdainful of Trump. Unlike Sens. Bob Corker (Tenn.) and Jeff Flake (Ariz.), both of whom took half-hearted stabs at Trump, Romney has very little to lose.

In fact, he has something significant to gain. Right now, the first line of Romney's obituary will probably describe him as "the former Massachusetts governor who lost the 2012 presidential race to Barack Obama." Now there's a chance to rewrite that description as "the Utah senator who bounced back from losing the presidency to help lead opposition to a notoriously destructive president from his own party." Romney has the chance to lead Republicans away from Trumpism and secure a positive mention for himself in the history books in the process. Even if he fails, his legacy probably grows by digging in against Trump — does anybody want to bet that history will smile upon this presidency?

If Romney's resistance is going to work, though, he and Democrats each owe something to one another.

For his part, Romney needs to admit his role in helping create the monster with which he now wants to do battle. In 2012, remember, Romney very publicly sought out and received Trump's endorsement for president, thus validating Trump as a legitimate power player in the GOP — this at a time when Trump had already displayed significant racist and dishonest behavior with his "birther" crusade against President Barack Obama. If Romney is going to have any credibility now, he needs to explain that moment — and explain if thinks he was wrong then, or if something has changed in the meantime.

Democrats, on the other hand, might do well to adjust their expectations. Liberals have often seemed to think that Never Trump Republicans are hypocrites because they dislike Trump and yet still vote for tax cuts and conservative judges. That's an impossible standard: Even Trump-hating conservatives are going to agree with the president on those kinds of policies, and Romney signaled Tuesday he'll be no different. "It is not that all of the president's policies have been misguided," Romney wrote. "But policies and appointments are only a part of a presidency." It's probably best to hold Romney to his word that he'll oppose the president in some significant areas, but not all of them.

It's possible the op-ed will amount to very little. The GOP and its base, after all, seem pretty devoted to Trump — Romney's own niece, in fact, is chair of the Republican National Committee under Trump, a sign of how completely the mainstream party apparatus has been co-opted by Trump's formerly insurgent candidacy. (The Romneys will join George and Kellyanne Conway as having the most interesting family dinners in Washington.) And Romney is known for occasionally speaking loudly and carrying a tiny stick — he spoke out against Trump's candidacy in 2016, but then let himself be humiliated for consideration as part of Trump's Cabinet. Even after that, Trump endorsed Romney's Senate bid, which Romney didn't exactly repudiate. Romney can sometimes be reminiscent of the guard dog who has a loud bark but quickly rolls over for a belly rub from strangers.

Then again, it's possible Romney has already painted himself into a corner: His op-ed is a repudiation of Trump that the president is unlikely to forgive or forget, and which Romney won't easily back away from. For better or worse, Mitt Romney has joined the resistance. The real question is if he'll make it matter.

Editor's note: This piece originally mischaracterized the relationship between Ronna McDaniel and Mitt Romney. It has since been corrected. We regret the error.